1. Field of the Invention
The invention relates to the field of composite structure fabrication techniques and, in particular, to a process for forming curves in woven composite preforms.
2. Description of Related Art
Typically T shaped composite structures are fabricated by joining the vertical member to the horizontal member by bonding a multi-number of reinforcing sheets across the joint (extending from the horizontal member up along the side of the vertical member). Such a joint is disclosed in WIPO Publication WO 01/64387 A1 Production, Forming, Bonding Joining And Repair Systems For Composite And Metal Components by N. Graham. Two honeycomb sheets are joined by layers of composite cloth to the horizontal member on each side of the vertical member that extend up each side of the vertical member. The disadvantage is that the joint's strength is dependent on the layers of composite cloth.
Recently, three-dimensional weaving has allowed very complex shapes to be woven. For example, U.S. Pat. No. 6,007,319 Continuous Forming Of Complex Molded Shapes by T. L. Jacobson, et al. discloses a method of weaving complex preform shapes. More recently a process for making woven 3D PI cross-section shapes in U.S. Pat. No. 6,446,675 Minimum Distortion 3D Woven Preforms by J. Goering. Such preforms can be impregnated with a resin and partially cured (called B stage) and stored for relatively long periods at low temperature until use is required. However, attempts to use such a preform in a curved structure has resulted in severe distortion. It is also difficult to form 2 dimensional woven composite preforms into curved shapes.
Thus, it is a primary object of the invention to provide a process for making curved preforms from woven composite materials.
It is another primary object of the invention to provide a process for making curved 3D woven PI preforms structures.
It is a further object of the invention to provide a process for making such 3D woven PI preforms in curved structures that does not significantly reduce the strength of the preform.